docs: def _filter_by_statement(self, statement):
          """Filter the data collection based on a conditional statement."""
          self.__class__._check_conditional_statement(statement, 1)
          _filt_values, _filt_datetimes = [], []
          for i, a in enumerate(self._values):
              if eval(statement, {'a': a}):
                  _filt_values.append(a)
                  _filt_datetimes.append(self.datetimes[i])
          return _filt_values, _filt_datetimes